how to determine if the service exists in shell [duplicate] - shell

Question

What is the best way in bash to check if a service is installed? It should work across both Red Hat (CentOS) and Ubuntu?
Thinking:
service="mysqld"
if [ -f "/etc/init.d/$service" ]; then
# mysqld service exists
fi
Could also use the service command and check the return code.
service mysqld status
if [ $? = 0 ]; then
# mysqld service exists
fi
What is the best solution?

Answer 1

To get the status of one service without "pinging" all other services, you can use the command:
systemctl list-units --full -all | grep -Fq "$SERVICENAME.service"
By the way, this is what is used in bash (auto-)completion (see in file /usr/share/bash-completion/bash_completion, look for _services):
COMPREPLY+=( $( systemctl list-units --full --all 2>/dev/null | \
awk '$1 ~ /\.service$/ { sub("\\.service$", "", $1); print $1 }' ) )
Or a more elaborate solution:
service_exists() {
local n=$1
if [[ $(systemctl list-units --all -t service --full --no-legend "$n.service" | sed 's/^\s*//g' | cut -f1 -d' ') == $n.service ]]; then
return 0
else
return 1
fi
}
if service_exists systemd-networkd; then
...
fi
Hope to help.

Answer 2

Rustam Mamat gets the credit for this:
If you list all your services, you can grep the results to see what's in there. E.g.:
# Restart apache2 service, if it exists.
if service --status-all | grep -Fq 'apache2'; then
sudo service apache2 restart
fi

Answer 3

On a SystemD system :
serviceName="Name of your service"
if systemctl --all --type service | grep -q "$serviceName";then
echo "$serviceName exists."
else
echo "$serviceName does NOT exist."
fi
On a Upstart system :
serviceName="Name of your service"
if initctl list | grep -q "$serviceName";then
echo "$serviceName exists."
else
echo "$serviceName does NOT exist."
fi
On a SysV (System V) system :
serviceName="Name of your service"
if service --status-all | grep -q "$serviceName";then
echo "$serviceName exists."
else
echo "$serviceName does NOT exist."
fi

Answer 4

In systemd (especially in Debian), it doesn't seems to work properly using the various answers from here. For some services like pure-ftpd if it's in disabled mode, it will not show up in service list when you trigger this command:
systemctl --all --type service
and when you start again the pure-ftpd with systemctl start pure-ftpd the list will appear again. So listing the service using systemctl --all --type service will not work for all services. Take a look at this for more information.
So, this is the best code so far (improvement from #jehon's answer) to check if a service is exist (even it has status inactive, dead or whatever status it is):
#!/bin/bash
is_service_exists() {
local x=$1
if systemctl status "${x}" 2> /dev/null | grep -Fq "Active:"; then
return 0
else
return 1
fi
}
if is_service_exists 'pure-ftpd'; then
echo "Service found!"
else
echo "Service not found!"
fi
Explanation:
If systemctl status found a service, it must have a text 'Active:' we filter using grep and it would return 0. If there is no 'Active:' text it would return 1.
If systemctl status does not find the 'Active:' text, it will print out a standard error. So, I put redirection 2> /dev/null to redirect the standard error. For example, if you are looking for the non existence service, you would get this error message if you don't put that error redirection:
Unit pure-ftpdd.service could not be found.
We don't want to have the above standard error message if you are doing scripting
EDIT:
Another method is to list out unit files which able to detect disabled service as pointed by #Anthony Rutledge for Debian system:
systemctl list-unit-files --type service | grep -F "pure-ftpd"
But using this method will not always work especially for older system because some unit files might not be detected using this command as explained in here. Also, using this method is slower if you have large unit-files that need to be filtered (as commented by #ygoe about heavy load on a small computer).

Answer 5

To build off of Joel B's answer, here it is as a function (with a bit of flexibility added in. Note the complete lack of parameter checking; this will break if you don't pass in 2 parameters):
#!/bin/sh
serviceCommand() {
if sudo service --status-all | grep -Fq ${1}; then
sudo service ${1} ${2}
fi
}
serviceCommand apache2 status

Answer 6

After reading some systemd man pages ...
https://www.freedesktop.org/software/systemd/man/systemd.unit.html
... and systemd.services(5)....
... and a nice little article ...
https://www.linux.com/learn/understanding-and-using-systemd
I believe this could be an answer.
systemctl list-unit-files --type service
Pipe to awk {'print $1'} to just get a listing of the service units.
Pipe to awk again to get the service names exclusively. Change the field separator to the period with -F.
awk -F. {'print $1'}
In summary:
systemctl list-unit-files --type service | awk {'print $1'} | awk -F. {'print $1'}
With variation and augmentation of the base solution, you can determine the state of your system's services by combining a for loop with systemctl is-active $service.

Answer 7

#!/bin/sh
service=mysql
status=$(/etc/init.d/mysql status)
print "$status"
#echo $status > /var/log/mysql_status_log

Answer 8

var=$(service --status-all | grep -w "$Service")
if [ "output" != "" ]; then
#executes if service exists
else
#executes if service does not exist
fi
$Service is the name of the service you want to know if exists.
var will contain something like
[+] apache2
if the service does exist

Answer 9

if systemctl cat xxx >/dev/null 2>&1; then
echo yes
fi

Answer 10

Try this, as ps command can be used in both Ubuntu&RHEL, this should be work in both platform.
#!/bin/bash
ps cax | grep mysqld > /dev/null
if [ $? -eq 0 ]; then
echo "mysqld service exists"
else
echo "mysqld service not exists"
fi